1. Field of the Invention
The present invention relates to a microcomputer.
2. Description of the Related Art
As an electronic control unit (ECU) utilizing a microcomputer, there is provided a unit of the same type which executes the predetermined processes after a constant time has passed from the predetermined time. Measurement of such constant time is called a timer process, while a function including the timer process which is executed by the microcomputer is called a timer function. For example, such function may be realized by an ECU which executes necessary communication with a communication partner after the predetermined time has passed from transmission of a drive signal to an apparatus of the communication partner or by an ECU which executes operations for driving an electrical load such as a lamp or a buzzer or the like after the predetermined time has passed from detection of change of a signal from an external switch or the like into an active level. However, such timer process essentially requires continuous measurement of time which results in large power consumption of the microcomputer.
Meanwhile, a certain ECU continuously monitors an external signal level of a microcomputer to realize a signal interlocking function with which the predetermined process is executed when a signal level reaches the predetermined level. However, such continuous monitor of signal level with the microcomputer requires a large amount of power consumption of this microcomputer. Moreover, for the monitoring of signal level, a noise canceling process also requires a large amount of power consumption.
On the other hand, another ECU is provided with a communication function executing the process through communication with the other ECU or the like. However, such communication may be realized after a certain waiting period for communication to prepare for a communication partner or a communication device. Therefore, power consumption of a microcomputer increases during such preparation period.
For example, in the case of an ECU which will be loaded to a vehicle, since a battery is not charged when an engine stops, such ECU with a microcomputer which requires a large amount of power consumption usually exhausts a battery.